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Carleton professors, alumni once more involved in gravitational wave detection

September 27, 2017 at 11:49 am
 Illustration of two black holes orbiting each other. Eventually the black holes will merge, producing gravitational waves

 Illustration of two black holes orbiting each other. Eventually the black holes will merge, producing gravitational waves

Photo: Alamy Stock Photo

Carleton College professors Nelson Christensen and Jay Tasson, along with alumni Jacob Broida ’17, Tom Callister ’13, Santiago Carides ’08, and Michael Coughlin ’12, all are authors on a newly-released paper describing a recent three-detector observation of gravitational waves from a binary black hole coalescence.

“What is unique about this detection is that in addition to the two American LIGO detectors (one in Washington State, the other in Louisiana), the European detector, Virgo (Cascina, Italy, just outside of Pisa), has also observed these gravitational waves,” Christensen revealed. “This is the first time that gravitational waves have been detected simultaneously in three detectors.”

The detection was announced today at the G7 meeting in Turin, Italy. The paper, “GW170814: A three-detector observation of gravitational waves from a binary black hole coalescence,” has been accepted for publication in Physical Review Letters. Christensen, the George H. and Marjorie F. Dixon Professor of Physics, assistant professor of physics Tasson, and the four alumni are all authors on this paper.

The gravitational waves were observed on August 14, 2017. The system consisted of two black holes with initial masses of 30.5 and 25.3 solar masses, 1.76 billion light-years away. The final black hole has a mass of 53.2 solar masses, meaning that a total of 2.7 solar masses were converted into energy associated with gravitational waves.

Using the two LIGO detectors, the location of the source on the sky could be constrained to a large patch of 1160-square degrees, but by including Virgo to the network the sky location was decreased to 60-square degrees.

The parameter estimation techniques used to produce estimation of these values were introduced into the LIGO Scientific Collaboration by Christensen in 1999. The Carleton team has also contributed to data quality studies for LIGO and Virgo that have helped to add confidence in these detections.

“With Virgo’s entry into the world-wide network of gravitational wave detectors, we have a very good chance to look for electromagnetic counterparts to these events,” Christensen explained. “Astronomers will have a smaller area in the sky to scan. Virgo’s detection is also gratifying personally. I spent a sabbatical year, 2005-2006, at the Virgo detector helping to bring the detector into operation. I have collaborated closely with Virgo since that time.”

As students, Coughlin and David Miller ’13 each spent a summer at the Virgo detector conducting gravitational wave detection research.

“The significantly improved sky-localization provided by the addition of Virgo, and the associated improved potential for detecting electromagnetic counterparts, has exciting implications for tests of general relativity,” Tasson said. “Searches for violations of fundamental symmetries in general relativity are the focus of my research, and these new observational capabilities provide promising new tools for that search.”

In the coming years, the world-wide gravitational wave detector network should grow with the addition of the Japanese detector, KAGRA, in 2019, and a third LIGO detector in India, in 2024. This will further increase the ability to detect gravitational waves and determine the location of the source.

Gravitational wave research at Carleton College is support by a National Science Foundations grant, PHY-1505373.

LIGO is funded by the NSF, and operated by Caltech and MIT, which conceived and built the project. Financial support for the Advanced LIGO project was led by NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council), and Australia (Australian Research Council) making significant commitments and contributions to the project. More than 1,200 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. Additional partners are listed at http://ligo.org/partners.php. The Virgo collaboration consists of more than 280 physicists and engineers belonging to 20 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; eight from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in The Netherlands with Nikhef; the MTA Wigner RCP in Hungary; the POLGRAW group in Poland; Spain with the University of Valencia; and EGO, the laboratory hosting the Virgo detector near Pisa in Italy.